Diagnostic and therapeutic challenges of acquired thyrotropic deficiency.

The acquired thyrotropic deficiency (TD) is a hypothyroid condition due to an insufficient stimulation by thyrotropin (TSH) of an otherwise normal thyroid gland. This disease can be the consequence of disorders affecting either the pituitary gland or the hypothalamus, but most frequently both of them, and is generally called central hypothyroidism (CH). CH is about one thousand folds rarer than primary hypothyroidism (PH) and the thyroid hormone defect is often less severe than in primary forms. Differently to PH, the TD is most frequently characterized by low/normal TSH levels and thyroid hormone replacement is associated with the suppression of residual TSH secretion. Thus, CH diagnosis and management often represent a clinical challenge because physicians cannot rely on the systematic use of the reflex TSH determination. The clinical challenge of CH is further amplified by the frequent combination with other pituitary deficiencies.